DESIZING || HYDROLYTIC DESIZING

What does Desizing mean and sizing material?

‘Size’ is imparted to the warp yarn before weaving so that breakage or damage of warp yarns will be less during weaving. The presence of size on the material makes it stiff and renders its treatment with different liquors utilized in dyeing and finishing difficult.

Therefore, one among the initial steps in wet processing is that the elimination of size and water-soluble admixtures, the operation being called desizing.

Sizing Ingredients

Sizing paste contain a number of chemicals.

1.) Adhessive material like corn, rice, starch etc.

2.) Lubricants/Softener:- Animal fats, mineral oils etc.

3.) Weighing material (china clay, sodium phosphate).

4.) Antiseptic Material (zinc chloride) added to yarn.

5.) Surfactant (soap) needs to be used.

6.) Anti bacterial chemical used to avoid bacteria, fungi etc.

Methods of Desizing

Two types of desizing are:-

1.) Hydrolytic- Starch is hydrolysed.

Starch (insoluble) → Dextrin (insoluble) → Dextrin (soluble) → Glucose → Maltose → Fructose

2.) Oxidative- Starch is oxidised.

Starch (insoluble) → Dialdehyde products and ketone (insoluble) → Hot alkaline Water.

Starch desizing methods can be classified as follows:

1.) Hydrolytic:-

(a) Rot Desizing:-

Grey Fabic → stored for 2hrs in water at room temp → washed

Only water is consider, no chemicals.
Cost is very less.
Not require any experts.
Require huge space for storing 24 hrs.
Removal of size is upto 50% hardly.

(b) Acid Desizing :-

Grey Fabic → impregnated with 0.25% H2SO4, HCL(stored for 24hrs) → washed

Cost is less but more than rot desizing.
Acid attacks cellulose and degrade it.
Channeling of liquor from top to bottom.

It is the most commonly use method globally. Enzymes act as catalyst. They don't take participate in reaction but help in completion of reaction. PH should be in between 5-7 and temperature maintain between 50-70°C.

Enzymes classified in to two types namely

i) Animal Enzymes: Collected from slaughterhouse waste such as pancreas.

ii) Vegetable Enzymes:

Malt extracted from germinated α-β amylase (20:80) barley.
Bacterial:- Cultivated bacteria such as α-amylase.

NOTE:- Starch consist of α-amylose 10%-20% and β-amylose (amylopectin) 90%-80%. α-Amylose is water soluble whereas β-amylose is water insoluble. α-amylose attack at random and reduces D.O.P (degree of polyemrization) while β-amylose only attacks at terminal point and produce glucose, maltose, sucrose.

Application of Enzymes